The invention resides in the use of a carbonaceous material in conjunction with an electron collector as an electrode for secondary electrical energy storage devices. The carbonaceous material of the electrode, is stable in the presence of an electrolyte system containing anions such as perchlorates, hexafluoroarsenates, and the like, under ambient or normal operating temperatures of use of the electrode. That is to say, the carbonaceous material does not appreciably irreversibly swell or contract during deep electrical charge and discharge cycles such as may be performed in the operation of a secondary electrical energy storage device.
Numerous patents and technical literature describe electrical energy storage devices utilizing carbonaceous material such as carbon or graphite as an electrode material. Of course, one of the earliest of these devices was the Laclanche' battery of 1866 wherein carbon was used as an electron collector in a Zn/NH.sub.4 Cl/MnO.sub.2 primary battery. Since then carbon has been used extensively as a component of the electrode in primary batteries, primary fuel cells, secondary fuel cells, secondary batteries and capacitors. The function of the carbon or graphite in these aforementioned devices has been primarily that of a current collector or as a reactive material to form new compounds with fluorine which have different structures and properties than the original carbon/graphite, and most recently, as semiconductor materials which form salts with ions of the electrolyte. These prior art devices can be categorized as: primary batteries such as is disclosed in Coleman et al. in U.S. Pat. No. 2,597,451, Panasonic Lithium Battery literature, and U.S. Pat. Nos. 4,271,242, 3,700,502, and 4,224,389; fuel cells, such as Japanese Publication No. 54-082043; and, secondary fuel cells, with limited rechargeability, such as is described in Dey et al. U.S. Pat. No. 4,037,025, a rechargable fuel cell employing an activated (high surface area) graphite; rechargable secondary batteries (accumulators) such as is disclosed in Hart U.S. Pat. No. 4,251,568 employing graphite as a current collection , and Bennion U.S. Pat. Nos. 3,844,837 and 4,009,323 and capacitors such as in Butherus et al. U.S. Pat. No. 3,700,975 or German Pat. No. 3,231,243 using a high surface area carbon (graphite).
Some of these devices also utilize ionizable salts dissolved in a nonconductive solvent.
The carbonaceous materials described in the patents and in the literature are materials graphitized or carbonized until the materials become electrically conductive. These materials are derived from polyacetylenes, polyphenylenes, polyacrylonitriles, and petroleum pitch which have been heated to "carbonize and/or graphitize" the precursor material to impart some degree of electrical conductivity. Some of the graphites used in the prior art literature are graphites such as RPG (Reinforced Pyrolytic Graphite), R-1 nuclear reactor grade graphite, PGCP (Pyrolytic Graphite Carbon Paper), and GRAFOIL (a Trademark of the Union Carbide Corporation) comprising an expanded and compressed graphite, and the like.
Doping of analogous carbonaceous materials has also been reported in Chemical and Engineering News, Volume 60, No. 16, pp. 29-33, Apr. 19, 1982, in an article entitled "Conducting Polymers R & D Continues to Grow"; Journal Electrochem Society, Electrochemical Science, 118, No. 12, pp. 1886-1890, December 1971; and Chemical & Engineering News, 59, No. 41, pp. 34-35, Oct. 12, 1981, entitled "Polymer Cell Offers More Power, Less Weight".
The problems attendant with these reported cells are that they do not have a long life since the electrode made from such carbonaceous material is susceptible to degradation when subjected to repeated electrical charge and discharge cycling.
For example, U.S. Pat. No. 3,844,837 (Bennion et al.) describes a battery employing a nuclear grade graphite impregnated with chips of Li.sub.2 O as the positive electrode and copper as the negative electrode in a LiCF.sub.3 SO.sub.3 -dimetyl sulfite (DMSU) electrolyte. The graphite electrode was made from a grade R-1 nuclear graphite (sold by Great Lakes Carbon Company) and was reported to be flaky after 9 cycles of electrical charge and discharge. The patentees also tested a graphite cloth and concluded it to be unsatisfactory. Several other graphites were used with equally unsatisfactory results with the best results obtained from pyrolytic graphite which failed after 33 cycles. In Dey et al. who employs a high surface area carbon or graphitic material, within the pores of which the chemical reaction occurs, is generally thought to be of a low conductance through lack of continuity of the carbon surface. Further, it is believed that such materials do not maintain the dimensional stability and structural integrity necessary for the reversible formation of carbon complexes required for long rechargeable cycle life of secondary batteries.
Experiments conducted in the course of the development of the present invention included the use of GRAFOIL (Trade Mark) which failed on the first electrical charge and RPG (Super Temp) graphite electrodes which also failed. It was found that an amount greater than 20% of the positive electrode made from RPG graphite was lost as flakes, chips and powder after only 27 electrical charge and discharge cycles.
It is to be noted that the prior art identifies the disintegration and damage to the electrode as being a result of a swelling and shrinking of the electrode body and that this swelling and shrinking increases with each electrical charge and discharge cycle which distorts the graphite platelets which flake off due to the stress of swelling and shrinking. In conducting these experiments in the course of the development of the present invention, it was confirmed that such flaking-off of the graphite platelets occurs when the aforementioned graphite materials were subjected to repeated electrical charge and discharge cycles.